Soong: Add synopsis to ndk_prebuilt_* modules.

Added synopsis to the following modules under cc package:
   * ndk_prebuilt_object
   * ndk_prebuilt_static_stl
   * ndk_prebuilt_shared_stl

Bug: b/128337482
Test: Generated the documentation and verified that the synopsis was
added to each of the module.

Change-Id: Icca7418268a0328b622014da8a077b26800075fd